Method and apparatus to produce synthesis gas via flash pyrolysis and gasification in a molten liquid

ABSTRACT

Disclosed are a method and a corresponding apparatus for converting a biomass reactant into synthesis gas. The method includes the steps of (1) heating biomass in a first molten liquid bath at a first temperature, wherein the first temperature is at least about 100° C., but less than the decomposition temperature of the biomass, wherein gas comprising water is evaporated and air is pressed from the biomass, thereby yielding dried biomass with minimal air content. (2) Recapturing the moisture evaporated from the biomass in step 1 for use in the process gas. (3) Heating the dried biomass in a second molten liquid bath at a second temperature, wherein the second temperature is sufficiently high to cause flash pyrolysis of the dried biomass, thereby yielding product gases, tar, and char. (4) Inserting recaptured steam into the process gas, which may optionally include external natural gas or hydrogen gas or recycled syngas for mixing and reforming with tar and non-condensable gases. (5) Further reacting the product gases, tar, and char with the process gas within a third molten liquid bath at a third temperature which is equal to or greater than the second temperature within the second molten liquid bath, thereby yielding high quality and relatively clean synthesis gas after a relatively long residence time needed for char gasification. A portion of the synthesis gas so formed is combusted to heat the first, second, and third molten liquid baths, unless external natural or hydrogen gas is available for this use.

CROSS-REFERENCE TO RELATED APPLICATIONS

Priority is hereby claimed to provisional application Ser. No.60/913,681, filed Apr. 24, 2007, which is incorporated herein byreference.

GOVERNMENT SUPPORT STATEMENT

This invention was made with United States government support awarded bythe following agency: USDA/FS 06-JV11111136-103. The United States hascertain rights in this invention.

FIELD OF THE INVENTION

The invention is directed to a method and corresponding apparatus toproduce synthesis gas from solid biomass by pyrolyzing and gasifying thebiomass in a pool of liquid metal.

BACKGROUND

Since the early 1900's, efforts have been made to develop an efficientmeans to convert solid, carbon-containing reactants into liquid fuels.The early work in the field was performed in Germany in the years priorto and between the two world wars. In 1912-13, Frederick Bergiusdescribed the fundamental process for hydrogenating coal under very highpressure to yield liquid fuels. (Bergius was awarded a one-half share ofthe 1931 Nobel Prize in chemistry for this work. Carl Bosch, a titan ofthe German chemical field, was awarded the other half.) Bergius' “directliquefaction” of coal was used to produce liquid fuels in Germany duringboth world wars. A decade after Bergius' work, Franz Fischer and HansTropsch, while at the Kaiser Wilhelm Institute, developed the chemistrythat now bears their names, and is sometimes referred to as “indirectliquefaction.” The general Fischer-Tropsch synthesis is ametal-catalyzed reaction to produce liquid hydrocarbons from a feedstockcomprising hydrogen and carbon monoxide. The feedstock is universallyreferred to as synthesis gas, or simply “syngas.” The syngas itself isderived from the partial combustion of methane or from the gasificationof coal or other biomass. The general reactions are as follows:

CH₄+½O₂→2H₂+CO(2n+1)H₂+nCO→C_(n)H_(2n+2)+nH₂O

The worldwide depression of the 1930's placed a severe economic strainon German companies' early efforts to build large-scale coalgasification plants. As the depression lingered on, crude oil pricesplunged to 10 cents per barrel, resulting in a worldwide glut of cheapoil. Two developments, however, stemmed the collapse of the nascent goalgasification industry: (1) the rise of the Nazi government; and (2) theconsolidation of the entire German chemical enterprise into an enormous,centrally-organized cartel (I. G. Farben). Begun in 1925, the formationand growth of I. G. Farben and its influence on the development of coalgasification technology can hardly be understated. Underwritten by theNazi government, and backed by the full might of Germany's preeminentchemical and industrial prowess, German efforts to convert its coalriches into liquid fuel continued unabated throughout the 1930's.

These efforts were vastly expanded during the years of World War II(1939-1945), as Germany was increasingly denied access to sources ofcrude oil. Synthetic liquid fuels produced from coal gasificationaccounted for roughly half of Germany's total production of fuel nearthe end of the war—124,000 barrels per day from 25 plants at its peaknear the end of 1944. At that point, synthetic fuel accounted for 92% ofGermany's aviation gasoline. (Intense allied bombing of German syntheticfuel plants began in earnest in late 1944 and early 1945. The resultswere immediate and fatal for the German war machine. In February 1945,Nazi Germany produced roughly a thousand tons of synthetic aviationgasoline—about one half of one percent of the level of the first fourmonths of 1944. Hostilities in Europe ceased in May of 1945.) See U.S.Department of Energy, “The Early Days of Coal Research.”

After World War II, efforts to gasify coal and biomass stagnated as hugereserves of crude oil were discovered and exploited in the Middle East,Venezuela, Nigeria, and elsewhere. The formation of another cartel, theOrganization of Petroleum Exporting Countries (OPEC), and its exerciseof pricing power in crude oil markets rejuvenated the coal and biomassgasification field. Founded in 1960 by Iran, Iraq, Kuwait, Saudi Arabiaand Venezuela (and later joined by Qatar, Indonesia, Libya, UAE,Algeria, Nigeria and Angola), OPEC did not rise to prominence until1973, when the Arab members of OPEC instituted an oil embargo that sentcrude oil prices skyrocketing. The Islamic fundamentalist revolution inIran in 1979 sent crude oil prices briefly into the stratosphere ($100per barrel when adjusted for inflation to January 2007). The mid-1980's,however, saw an equally dramatic drop in oil prices from their 1979highs. Continued political instability in the middle east starting withthe 1991 Gulf War, and extending to the panic caused by the Sep. 11,2001 terrorist attacks in the U.S. (and the subsequent U.S. invasion andoccupation of Iraq), coupled with the rapid industrialization of Chinaand India, have combined to maintain current crude oil prices at veryhigh levels.

From a technological standpoint, developments in coal and biomassgasification have proceeded along many fronts. For example, U.S. Pat.No. 2,459,550, issued Jan. 18, 1949, to A. J. Stamm, describes anapparatus for continuous destructive distillation of solids (principallywood in the form of sawdust or chips, and coal in the form of coal dustor pea-sized particles) in a bath of molten metal. The material to begasified is carried between two finely porous, continuously loopedscreens that pass beneath the surface of a pool of liquid metal. Theheat from the liquid metal is rapidly transferred to the material.Volatile compounds within the material are thereby vaporized, and thevapors pass through the porous screen, rise through the molten metal,and are then condensed. Both the resulting condensate and the charredsolid material are then recovered. Similar, single-bath devices aredescribed in U.S. Pat. Nos. 4,649,867; 4,925,532; and 5,693,188.

U.S. Pat. No. 3,647,379, issued Mar. 7, 1972, to Wenzel et al. describesa device for gasifying a coal/water mixture. The device is asingle-chamber device in which dehydration of the coal is followed bygasification of the dried coal and then endothermic reaction of theresulting gas products.

U.S. Pat. No. 4,126,668, issued Nov. 21, 1978, to Erickson, describes amethod to produce a hydrogen-rich gas such as pure hydrogen, ammoniasynthesis gas, or methanol synthesis gas by reacting steam with anon-gaseous intermediate, whereby some of the steam is reduced tohydrogen and some of the intermediate is oxidized. Carbon dioxide may beadded to (or substituted for) the steam, whereby carbon monoxide isproduced in addition to (or in lieu of) H₂. The oxidized intermediate isreduced by a reducing gas. The reducing gas is generated by partiallyreforming a light hydrocarbon such as natural gas or naphtha with steamand/or CO₂, and then partially oxidizing the partially reformed gas withair. The low BTU exhaust gas resulting after reduction of theintermediate oxide is used as fuel for the primary reformer. Whenammonia synthesis gas is produced by this process, the purge and flashgases from the ammonia synthesis loop are added to the reducing gas.

U.S. Pat. No. 4,344,773, issued Aug. 17, 1982, to Paschen et al.describes an apparatus for gasifying carbon-containing media. The deviceincludes a molten iron both for gasifying the reactants and a pluralityof nozzles for introducing the reactants into the molten iron bath. Anoutlet is also provided for removing slag from the bath. Because it usesmolten iron, this device has distinct drawbacks. Melting the ironrequires an extremely high reactor temperature. This, in turn, spawnsother considerations. For example, the high temperature of the molteniron is extremely detrimental to the reactor lining. To ensure longlining life requires essentially zero motion of the iron melt.

Likewise, the liquid slag is very difficult to handle due to the extremetemperatures involved. The process also is not energy efficient becauseit is hard to obtain a quality syngas at such high temperatures.

U.S. Pat. No. 4,345,990, issued Aug. 24, 1982, describes a continuousmethod for recovering oil and gas from carbon-containing material. Theapparatus described here uses two molten-metal baths. No screens areutilized. Instead, the material to be gasified is placed directly intothe bath. The first bath is a comparatively low-temperature bathmaintained at about 500° C., while the second bath is maintained at amuch higher temperature of about 1,200° C. Two different metals,substantially insoluble in each other when melted, are used in the twobaths. Lead is the preferred metal for the first bath; iron is thepreferred metal for the second bath. The reactant material is depositedinto the first bath (molten lead), and the volatized gases arecollected. The molten lead, with the partially distilled carbonaceousmaterial within it, is then transferred to the second bath (molteniron). Here, oxygen is injected into the gas space above the molteniron. The carbonaceous material moves from the lead phase, to the ironphase, where it is further volatilized. The volatile gases liberatedfrom the solids react with the oxygen in the headspace above the molteniron. The molten lead (which is not soluble in the molten iron) settlesto the bottom of the second bath and is transferred back to the firstvessel. Of particular note in this method is that the thermaldecomposition in the first bath takes place in the absence of addedoxygen, while oxygen is purposefully added in the second thermaldecomposition. By recycling the lead that settles to the bottom of thesecond bath back into the first bath, the heat required to melt the ironis backward integrated to heat the lead too. In the second bath, theremaining amount of carbon in the solid reactant is gasified to syngasby adding a balanced amount of oxygen to the reaction (in the form ofoxygen gas, air, oxides, etc.). Any remaining solids are removed asslag. The principal drawback of this device is that it requires pumpingmolten metals from bath-to-bath. Thus, the device has numerousmechanical parts that operate at extremely high temperatures.

U.S. Pat. No. 5,085,738, issued Feb. 4, 1992, to Harris et al. describesan apparatus for gasifying organic waste materials. The apparatusincludes an elongated and inclined chamber filled with molten lead.Organic material introduced in a lower portion of the chamber migratesthrough the molten lead to a higher portion of the chamber due to theorganic material having a specific gravity less than the molten lead. Asthe organic material migrates through the molten lead, the material isgasified. The resulting vapor-phase hydrocarbons are then captured in acondenser. The gaseous hydrocarbons are utilized to heat the lead in thechamber and the vapor is condensed to liquid hydrocarbons in thecondenser. Residual solids flow to a reservoir connected to the chamber.This apparatus described here is intended for processing tire scraps andgenerally operates in the temperature range of 340° C. to 510° C. Otherwaste material can be used (such as wood and paper products). However,the pyrolysis products of woody biomass will have high amounts of heavytar and char at this temperature range. The char would be difficult tomanage in this single-chamber reactor apparatus. See also Published U.S.Patent Application 2005/0 131 260.

U.S. Pat. No. 5,478,370, issued Dec. 26, 1995, to Spangler describes amethod for producing syngas from lower alkanes. In this approach, amolten metal oxide bath delivers oxygen to a feed stream containinglower alkanes. A reaction thus takes places wherein the lower alkanesare oxidized to produce carbon dioxide and the molten metal oxide isreduced to the elemental metal. The elemental metal is regenerated tothe metal oxide by contact with a regenerant such as air. Heat from themolten baths is transferred to an endothermic reactor where a portion ofthe carbon dioxide-containing gas is converted to a mixture of carbonoxides and hydrogen.

U.S. Pat. No. 6,051,110, issued Apr. 18, 2000, to Dell'Orfano et al.describes a partially integrated, continuous process (and correspondingapparatus) to distill carbonaceous materials. In a fashion similar tothe looped screens of the Stamm patent (see above), the Dell'Orfanopatent uses mesh baskets to convey the carbonaceous material through theprocess. Using the baskets also eases recovery of the solid productsthat remain after gasification. In this approach, the carbon-containingreactants (preferably wood) are passed first through a de-gassing bathcontaining heated liquefied volatiles recovered from earlier runs (andreferred to as “wood petrol” in the patent). The first bath degasses thewood without degrading the released gases. The de-gassed wood is thenpassed through a molten-metal bath (preferably molten lead), whichconverts the wood to char and volatiles. The volatiles are collected anda portion of them are recycled for use as the “wood petrol” in the firstdegassing bath. The remaining gases are collected. Lastly, the char isthen passed through a condensing bath. Oxygen is specifically excludedfrom the second and third baths.

U.S. Pat. No. 6,110,239, issued Aug. 29, 2000, to Malone et al.describes a two-zone process in which a high-pressure hydrogen-rich gasstream and a high-pressure carbon monoxide-rich gas stream aresimultaneously produced in separate zones using a molten-metal gasifier.Because the two gas streams are produced in separate zones, thisapproach eliminates the need to separate or compress the two gases. Theprocess as described includes introducing a hydrocarbon feed into amolten metal bath beneath the molten metal surface in a first feed zoneoperating at a pressure above five (5) atmospheres absolute, whichdecomposing the hydrocarbon feed into a hydrogen-rich gas, and carbon.The carbon dissolves in the molten metal. The carbon concentration inthe molten metal is carefully maintained to remain at or below the limitof solubility of carbon in the molten metal. A portion of the moltenmetal is then transferred from the feed zone to another molten metaloxidation zone operating at a pressure above five (5) atmospheresabsolute into which an oxygen-containing material is introduced. Thecarbon dissolved in the metal reacts with the introduced oxygen to forma carbon monoxide-rich gas which leaves the oxidation zone. Thus, thecarbon concentration in the molten metal is reduced. In this zone, thecarbon concentration in the molten metal is controlled so that it doesnot reach the concentration at which the equilibrium oxygenconcentration would exceed its solubility limit in the molten metal (inwhich instance a separate iron oxide phase would accumulate). A portionof the molten metal which has a lower carbon concentration from theoxidation zone is then recycled back to the feed zone. The two gasstreams are passed out of their respective zones. The main disadvantageof this approach is that the concentration of carbon and oxygen in thetwo zones must be very carefully controlled, or CO will contaminate theH₂ gas stream. If the oxygen exceeds its solubility limit in the secondzone of the molten metal, the oxygen will also react with thehydrocarbon in the first zone to create a CO impurity in thehydrogen-rich gases.

U.S. Pat. No. 6,663,681, issued Dec. 16, 2003, to Kindig et al.describes a method for producing hydrogen gas. The hydrogen gas isformed by reducing steam using a metal/metal oxide bath (e.g. iron/ironoxide) to remove oxygen from water. The steam is contacted with a moltenmetal mixture including a first reactive metal (iron) dissolved in adiluent metal (tin). The reactive metal oxidizes to the correspondingmetal oxide, forming a hydrogen gas (via reduction). The metal oxide canthen be reduced back to the metal for further production of hydrogenwithout substantial movement of the metal or metal oxide to a secondreactor.

U.S. Pat. No. 6,830,597, issued Dec. 14, 2004, to Green, describes aprocess and device for gasifying biomass. In this approach, heat from acombustion chamber is used to gasify or liquefy biomass. The combustionchamber partially surrounds a reactor tube and is in direct thermalcontact with the reactor tube. In this fashion, heat from the combustionchamber passes directly through the reactor wall to heat the biomasswithin the reactor tube.

U.S. Pat. No. 6,863,878, issued Mar. 8, 2005, to Klepper et al.,describes a method of producing syngas from biomass or othercarbonaceous material. The method utilizes a controlled devolatilizationreaction in which the temperature of the feed material is maintained atless than 232° C. (450° F.) until most of the available oxygen isconsumed. The reaction is carried out at this very low temperature tominimize pyrolysis of the feed material. The method backward integratesthe resulting syngas to provide the energy for the initial gasificationreaction. The approach does required using high-pressure,high-temperature (1,000° C.) high-pressured steam to gasify thelow-temperature biomass residues. This process is inefficient withrespect to converting the carbon in the biomass reactant into syngas.The residual air combusts with the feedstock. The resulting energy isused to heat the biomass to the required temperature. That carbon islost out the flue and is not converted to syngas.

Published U.S. Patent Application 2005/0 032 920, published Feb. 10,2005, to Norbeck et al., describes a multi-step, integrated, steampyrolysis apparatus for producing syngas for use as a gaseous fuel or asa feedstock for Fischer-Tropsch reactions. The process is described as“substantially self-sustaining.” Here, slurry of particles ofcarbonaceous material in water, and hydrogen, is fed into ahydro-gasification reactor under conditions that yield amethane-containing product gas. This methane-containing gas is then fedinto a steam pyrolytic reformer to yield syngas. A portion of thehydrogen generated by the steam pyrolytic reformer is fed through ahydrogen purification filter and backward integrated into thehydro-gasification reactor used in the first step. The remainingsynthesis gas generated by the steam pyrolytic reformer can be useddirectly as a fuel. Alternatively, the syngas may be fed into aFischer-Tropsch reactor to produce liquid fuels. Molten salt loops areused to transfer heat from the hydro-gasification reactor (and theFischer-Tropsch reactor if a liquid fuel is produced), to the steamgenerator and the steam pyrolytic reformer.

Very recently, a paper appeared in the Proceedings of the NationalAcademy of Sciences, Agrawal, Singh, Ribeiro & Delgass (Mar. 14, 2007)“Sustainable Fuels for the Transportation Sector,” PNAS,doi:10.1073/pnas.0609921104. This paper presents a much generalizedscheme for producing liquid fuels by producing hydrogen (H₂) fromcarbon-free primary energy source, e.g., solar, nuclear, wind. Thehydrogen so produces is then reacted with gasified solids, such as coalor biomass. The overall goal is the complete incorporation of everycarbon atom present in the reactant into a molecule of liquid fuelproduct. Carbon dioxide produced in the biomass gasification step isconstantly recycled into the reactor, thus eliminating the release ofcarbon dioxide into the atmosphere. It must be noted, however, that thepaper sets forth only a conceptual framework. As the authors themselvesstate, the chemical processing systems to accomplish the process “areyet to be defined.”

Thus there remains a long-felt and unmet need to produce liquid fuelsefficiently from biomass and other solid reactants.

SUMMARY

The gasifier apparatus described and claimed herein uniquely utilizes amolten liquid (e.g., a molten metal or ionic liquid) as a heat, mass,and reaction carrier to advance the biomass biorefinery viathermo-chemical processes. Because liquid metals and salts have veryhigh heat transfer rates and a wide range of operating temperatures,using them as energy carriers in a biomass gasifier provides significantadvantages in reducing the system complexity, size, and costs. Describedherein are two versions of a continuous gasifier for converting biomassinto syngas. The syngas can then be used in any fashion, but ispreferably integrated to a reactor using the well-understoodFischer-Tropsch synthesis to convert the syngas to a liquid synfuel,such as a fuel comprising alcohols and/or alkanes. The gasifierdescribed herein is designed to convert all or substantially all of thecarbon in the biomass feedstock into raw, high-BTU, and clean syngas.

This end is achieved by introducing multiple functionalities into thegasifier. Specifically, in the preferred versions, wet biomass isintroduced into naturally-pressured molten liquid slurry. (The moltenliquid can be a molten metal or a molten ionic liquid. Unless otherwisenoted, the term “salt” as used herein is synonymous with “molten ionicliquid.”) Alternatively, the apparatus incorporates a biomass drier thatefficiently pre-dries wet biomass at temperatures below degradation(<200° C.). The apparatus functions to cause effective pyrolyzing andcracking of tar in the hot (<1,000° C.) slurry zone. The resultingpressurized gas bubbles are reformed with backward integrated steam intosyngas. Contaminates such as sulfur and other elements are retained bythe molten liquid, where they can be removed by filtration. These andother sub-processes that interact with the molten liquid are detailed infull herein.

The present apparatus yields liquid fuels at levels near the theoreticalmaximum for a gasifier. That is, the current technology has a highsynfuel output from woody biomass that can be further increased by 60%or more on a self-sufficient energy basis, or by 100% or more ifexternal heat sources such as solar energy or combusting natural gas areused in the gasifier. The synfuel yield of the device can be greatlyincreased (by 191% or more) if external hydrogen gas sources are alsoused as feedstock to the gasifier (see also Tables 1 and 2).

The gasifiers are adaptable to these various levels of fuel output, withthe expense and scale of the apparatus rising with the productivitylevel. The specific sub-processes and the economics associated withoverall efficiency of the device will ultimately define the productioncost-per-gallon of the synfuel.

The present method and corresponding apparatus involves preparing thebiomass residue for the gasification/reformer stage in a manner thatallows all carbon in the feedstock to reach the syngas. This preparatoryprocess comprises two stages: A first, low-temperature drying stage todrive moisture and the non-combustible gases from the biomass reactant.(The water is recycled for steam injection in the pyrolysis/gasificationand/or gasification/reformer stages.) The second stage starts with afast pyrolysis step at a much higher temperature (generally 300° C. to1,200° C.). The heat for both stages is provided by one or more moltenliquid baths that are thermostatically maintained at the desiredtemperatures. Tar and non-condensing gases from the pyrolysis are mixedwith the process gas from the first stage and/or backward integratedsyngas and/or a natural gas feedstock (the mix comprises steam, H₂,CO_(X), or CH₄ but not N₂ or O₂). These gases are then reformed, and thedeveloping char gasified, at high pressures and temperatures within thebubbles that form in the fast-pyrolysis bath (and in the headspace abovethe pyrolysis chamber). This fast pyrolysis and partialgasification/reforming may take place in the absence of catalysts, or inthe presence of metallic catalysts to aid in driving the gasificationand reforming reactions to completion. Some examples of reactivemetallic catalysts include, without limitation: Ge, Fe, Zn, W, Mo, In,Sn, Co, Pb, and Sb. These metals form metal oxides by taking oxygen fromsteam and releasing H₂. The released hydrogen exothermically gasifiesthe char and hydrogenates the heavy tar. The metal oxide formedcirculates with the diluent metal to the gasification/reformer stage toprovide oxygen to react with the entering light hydrocarbons and anyremaining char to form more H₂ and CO for syngas. The availability ofnuclear- or solar-derived H₂ gas for mixing in with the process gascould also eliminate the use of reactive metallic catalysts.

A portion of the resulting syngas can then be backward integrated tofire the burner(s) for the drying chamber and the fast-pyrolysischamber. This use of backward integrated syngas can also be avoidedpartially or fully with the availability of a natural gas source and/orthe nuclear- or solar-derived H₂ gas to fire the burner(s). As noted inthe Detailed Description, the biomass reactant can be indirectlycontacted with the molten liquid using porous screens or porous tubes,in which case the molten baths are static. Alternatively, the biomassreactants may be directly contacted with the molten liquid and themolten liquid/biomass slurry moved from chamber to chamber.

The bench-scale tests described in the Examples show that the presentinvention yields a high quality syngas that can be obtained without theuse of catalysts and through thermal means only. (Catalysts, as notedabove, may also be used in the process, if desired. Any metal-containingcatalyst now known or developed in the future for catalyzing reformingreactions may be used in the present invention.) That is, the processcan operate in the absence of catalysts, preferably at temperatures lessthan about 1,000° C., and as low as about 950° C. (far below the meltingpoint of iron and the melting point of slag consisting of biomass ash).Ceramic-lined steel tanks have been successfully used at temperaturesbelow the melting point of iron (using lower temperature molten liquidssuch as lead) even when the metals are in motion to achieve heat andmass transfer of the feedstock. At temperatures of about 1,000° C. andlower, the non-reacting residues of biomass remain as solids, makingthem easier to remove (e.g., by skimming or using a cyclone separator).

A particular advantage of the present invention is that it can convertmixed biomass feedstocks into alkane fuels at high efficiency andwithout the need for an external water source. In the case of “generic”wood as an exemplary biomass reactant, the full conversion of wood tosyngas requires an enthalpy increase of 603 kJ/mol. (The overallreaction is C₆H₉O₄+2H₂O→6CO+6.5H₂. The combustion energy of theresulting syngas, however, is 3,250 kJ/mol. Thus, backward integratingonly 19% of the resulting syngas to heat the various molten metal bathsis all that is required to make the reactor self-sufficient. Theremaining 81% of the product syngas can then be used in conventionalfashion, e.g., for direct combustion in a generator, for Fischer-Tropschsynthesis, etc.

Moreover, because the apparatus is heavily insulated (to limit heatlosses), once the apparatus is brought to operating temperatures, thereis very little heat loss. Thus, roughly 1% of the syngas needs to becombusted to make up for molten liquid heat losses once the apparatus isup and running. Thus the present invention enables a one-pass, 80%efficient water-gas shift/Fischer-Tropsch reactor (with 20% of theresulting syngas being combusted to heat the gasifier). The conversionof the syngas to iso-octane involves an enthalpy release of −760 kJ/mol.Water is fully recovered and recycled into the process. At 80%efficiency then, the Fischer-Tropsch exothermic heat of 608 kJ/mol issufficient to dry the incoming biomass reactants. The moisture isrecycled for use in the gasification step. Electricity can be generatedfrom a fuel cell operating at the same temperature as the gasificationchamber. The electricity so generated can then be used to drive theauger, conveyers, and other ancillary equipment associated with theapparatus of the present invention. Thus, the device can be integratedinto a self-powered mobile unit. Biomass is the reactant. The resultingproducts are syngas (and liquid fuels made from the syngas),electricity, N₂ and CO₂ exhaust gases, and excess water.

Thus, the invention is directed to a method and corresponding apparatusfor making syngas from biomass. A first version of the apparatuscomprises a first molten liquid bath dimensioned and configured tomaintain a molten liquid at a first temperature suitable for drying abiomass reactant without degrading the biomass reactant. In this firstbath, wet biomass is dried to yield dried biomass and process gascomprising water (and other gases). The first bath is operationallyconnected to, and dimensioned and configured to transfer molten liquidand dried biomass contained therein toa second molten liquid bath. Thesecond bath is dimensioned and configured to maintain a molten liquid ata second temperature suitable for fast pyrolyzing the dried biomass toyield gas, tar, and char. The second bath is dimensioned and configuredto transfer molten liquid, and the gas, tar, and char contained thereinto a third molten liquid bath. This third bath is dimensioned andconfigured to maintain a molten liquid at a third temperature suitablefor reforming the gas, tar, and char into synthesis gas. The third bathis dimensioned and configured to transfer molten liquid, tar, and charcontained therein to a separator. The separator is dimensioned andconfigured to separate tar and char from the molten liquid to yieldclean molten liquid. The separator is also operationally connected tothe first molten liquid bath and is dimensioned and configured totransfer clean molten liquid back to the first molten liquid bath.Lastly, a conduit is operationally connects the first molten liquid bathto the third molten liquid bath. The conduit is dimensioned andconfigured to transfer process gas from the first molten liquid bath tothe third molten liquid bath. Because water from the raw biomass isrecycled into the third molten bath, an external source of water is notusually required (depending upon the initial moisture content of thebiomass).

A second version of the apparatus comprises a first molten liquid bathdimensioned and configured to maintain a molten liquid at a firsttemperature suitable for drying a biomass reactant without degrading thebiomass reactant, to yield process gas and dried biomass. A secondmolten liquid bath, dimensioned and configured to maintain a moltenliquid at a second temperature, and suitable for fast pyrolyzing thedried biomass to yield gas, tar, and char, is also provided. A thirdmolten liquid bath dimensioned and configured to maintain a moltenliquid at a third temperature suitable for reforming gas, tar, and charinto synthesis gas is also provided. A char crusher is interposedbetween the second molten liquid bath and the third molten liquid bath.The char crusher is dimensioned and configured to crush char intopowdered char. A conveyer assembly is provided to move reactants betweenthe various chambers. The conveyor is dimensioned and configured to: (a)move the dried biomass from the first molten liquid bath to the secondmolten liquid bath; (b) to move char from the second molten method bathto the char crusher; and (c) to move powdered char from the char crusherto the third molten liquid bath. As in the first version of theinvention, a conduit is provided that operationally connects the firstmolten liquid bath to the third molten liquid bath. The conduit isdimensioned and configured to transfer process gas from the first moltenliquid bath to the third molten liquid bath.

The inventive method is a method to convert a biomass reactant intosynthesis gas. The method comprises heating biomass in a first moltenliquid bath at a first temperature, wherein the first temperature is atleast about 100° C., but less than the decomposition temperature of thebiomass, wherein process gas comprising water and small amounts ofresidual air and volatile organic compounds (VOCs) is evaporated fromthe biomass, thereby yielding dried biomass. The process gas evaporatedfrom the biomass is captured. The dried biomass is heated in a secondmolten liquid bath at a second temperature, wherein the secondtemperature is sufficiently high to cause flash pyrolysis of the driedbiomass, thereby yielding product gases, tar, and char. Process gas canbe added at this point to enhance char gasification immediately afterthe pyrolysis event. The product gases, tar, and char are then reactedfurther with the process gas within third molten liquid bath at a thirdtemperature which is equal to or greater than the second temperaturewithin the second molten liquid bath, thereby yielding synthesis gas. Aportion of the resulting synthesis gas is combusted to heat the first,second, and third molten liquid baths (unless external natural gas orhydrogen gas is available to be combusted instead).

The portion of the synthesis gas used to heat the device itself can becombusted to heat the third molten liquid bath only. Heat from the thirdmolten liquid bath is then integrated to heat the second and firstmolten liquid baths (whose temperatures are lower than the third bath).The biomass reactants can be directly immersed into the various liquidbaths, or heated indirectly by placing the biomass reactants within asuitable porous container that allows gas to escape the container butprevents molten liquid from entering the container.

It is generally preferred that the temperature in the first bath is lessthan about 200° C., the temperature in the second bath is from about300° C. to about 800° C., and the temperature in the third bath is lessthan about 1,200° C.

It is preferred that when metals are used, the molten metal in each ofthe first, second, and third baths is the same and comprises a metalselected from the group consisting of Ga, In, Pb, and alloys thereof.The metal may be further alloyed with a metal selected from the groupconsisting of Bi, Cd, Tl, Sn, and combinations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a first version of the presentinvention.

FIG. 2 is a schematic diagram of a second version of the presentinvention.

FIG. 3A is a schematic diagram of a bench-scale gasifier according tothe present invention.

FIG. 3B is a schematic of another gasifier according to the presentinvention.

FIG. 4 is a graph depicting the average normalized pressure forpyrolization of wood samples using the test device depicted in FIG. 3A.

FIG. 5 is a graph depicting product gas concentrations for a test run at1,000° C. and using wood as the biomass reactant.

FIG. 6 is a graph depicting gas reaction rates and hold-up when usingthe present invention with a molten metal bath comprising a eutecticmixture of Bi (55.5 wt %) and Pb (44.5 wt %). The gas samples testedcomprised Ar (86.52%), CO₂ (0.504%), H₂ (3.960%), CH₄ (0.010%), CO(6.960%) and O₂ (0.48%). The experiments show that at temperatures up toabout 1,000° C., there are significant reactions with O₂, butessentially no reaction of H₂ or CO.

FIG. 7 is a graph depicting the net process emissions of CO₂, H₂O, O₂,and diesel from woody biomass.

FIG. 8 is a graph depicting potential synfuel productivity from woodybiomass, as a function of gasifier efficiency.

FIG. 9 is a graph depicting delivered biomass cost at $75 per dry ton,converted to feedstock cost per gallon of synfuel.

FIG. 10 is a graph depicting feedstock cost per diesel gallon for $75per dry ton of woody biomass and $0.70/kg to $2/kg of “green” H₂.

FIG. 11 is a graph depicting biomass required to displace U.S. oilconsumption (5 billion barrels/yr) for transportation.

DETAILED DESCRIPTION OF THE INVENTION Overview:

In light of political instabilities, a growing world population, and thethreat of global warming, there is strongly felt, worldwide emphasis ondeveloping technologies to derive synthetic fuels (“synfuel”) fromrenewable biomass. The present invention addresses this emphasis via amultiple-stage gasification apparatus. The first stage produces syngasby endothermic chemical reaction with gas-liquid separation processes(preferably in the absence of any catalysts) and the second stageproduces a liquid synfuel such as ethanol, gasoline, or diesel from thesyngas by exothermic processes involving a series of catalysts, gasseparations and steam insertion. The critical technology to enable thistwo-stage approach at suitably large-scales is a high-volume method toproduce syngas from biomass in the first stage of the process.

Fundamental mechanisms of biomass pyrolysis and gasification provide theclues to understanding the difficulty of producing syngas from biomass.As used herein, the term “syngas” refers to a gaseous mixture comprisedprimarily of CO and H₂, with additional minor components, including H₂O,CO₂, CH₄, N₂, and hydrocarbons. The term “biomass” refers to the organicmaterials produced by plants and animals, such as leaves, roots, seeds,and stalks, as well as microbial and animal metabolic wastes (e.g.,manure), without limitation. Common sources of biomass include (withoutlimitation): (1) agricultural wastes, such as corn stalks, straw, seedhulls, sugarcane leavings, bagasse, nutshells, and manure from cattle,poultry, and hogs; (2) woody materials, such as wood or bark, sawdust,timber slash, and mill scrap; (3) municipal waste, such as waste paperand yard clippings; (4) energy crops, such as poplars, willows, switchgrass, alfalfa, prairie bluestem, corn, soybean, and (5) coal, peatmoss, and the like. The term “biomass-derived reactant” refers to anyreactant that can be fabricated from biomass by any means now known ordeveloped in the future, including (without limitation) polysaccharides,monosaccharides, polyols, oxygenated hydrocarbons, sugars, starches, andthe like. The heating value of syngas is maximized when H₂O, CO₂ and N₂are either removed from the product stream or are prevented from formingin the first instance. Similarly, the heating value of syngas increasesin proportion to the ratio of hydrogen to carbon monoxide within thesyngas. The biomass reactants described in the Examples presented beloware lignocellulosic, and comprise approximately of 30% lignin (byweight) and 70% carbohydrate polymers (holocellulose) in the form ofhemi-cellulose (polymers of C5 and C6-carbohydrates that are readilyhydrolyzed to form simple sugars) and cellulose (mainly glucose polymersthat are difficult to hydrolyze). These reactants serve asrepresentative examples of biomass that can be used in the presentinvention.

For approximate analysis, holocellulose has been assigned the empiricalformula, C₆H₁₀O₅, and lignin has been assigned the empirical formula,C₉H₆O₂ (H₂O)(OCH₃)_(4/3). Both empirical formulas have a closecorrelation to their measured and calculated heat of combustion values.Dietenberger (2008) “Mechanistic Pyrolysis Kinetics of Solid RedwoodConstituents Using a Modified Cone calorimeter Test,” Fire SafetyJournal (in press). If the wood structure is theoretically reduced tomonomer units given by the empirical formulae (on a moisture-free,ash-free, and extractive-free basis) the molar fractions of lignin andholocellulose in woody biomass are, respectively, 25% and 75%. Thisgives an overall empirical formula for “generic” dry lignocellulose ofC₆H_(8.9)O_(4.1), which is in close agreement with the valueconventionally used by the biomass community. Henrich & Dinjus (2002)“Tar-free, high pressure synthesis gas from biomass,” Expert Meeting onPyrolysis and Gasification of Biomass, Strasbourg, France, 30 Septemberto 1 Oct. 2002.

In a conceptual process beginning with dry distillation traditionallyassociated with very slow heating rates, the H₂O is mainly taken out ofthe wood structure and what remains is a dry charcoal that retains mostof the combustion heat of wood (because the emitted steam has no heat ofcombustion). The dry distillation process can also be completed in amatter of minutes with other volatile gases besides steam also emittedby drawing the biomass between two 80-mesh stainless steel screensimmersed in a low-temperature, molten metal alloy bath at between 200°C. to 360° C. (depending on the quality of charcoal desired). See theStamm patent, supra. Temperatures higher than 360° C. are evidentlyavoided as it corresponds to breakdown of the lignin, thus giving riseto phenol-based molecules within the tar that have a greater tendencyfor gumming. The breakdown of lignin that releases phenol-basedmolecules at lower temperatures (less than 360° C.) is enhanced by thepresence of free moisture and air, which must be removed to avoidproduction of such gumming tar components. The fast pyrolysis process isalso more easily achieved by a prior removal of free moisture because ofthe high loading of evaporative heat.

The next processing step is char gasification with steam to producehigh-quality and approximately equimolar concentrations of CO and H₂ ataround 1100° C. and 1.0 bar pressure. This syngas has a Lower HeatingValue (LHV) of about 12.65 MJ/m³). Excessive steam levels will promotethe water-gas shift reaction, CO+H₂O→CO₂+H₂, which has the effect ofreducing the heat value of syngas unless steam can be condensed and CO₂removed. The economic drawbacks to the conventional approach include thelarge endothermic heating required, the slow reaction rates of carbongasification by steam as compared to direct pyrolysis, and the need foran external source of water.

If instead of dry distillation the dried biomass is dramatically heatedto between about 400° C. and about 600° C., then the pyrolysis producesabout 70 wt % tar and 10 wt % gas within the wood volatiles, and 20 wt %remaining as char (mostly carbon and ash). Because the volatilesproduced under these conditions tend to have the overall empiricalformula, (CH₂O)x, Dietenberger (2002) “Update for Combustion Propertiesof Wood Components,” Fire and Materials Journal, 26:255-267, theequilibrium chemical balance at 1,000° C. and 1.0 bar pressure indicatesthat this volatile mixture will reduce to equimolar concentrations of COand H₂. Syngas comprising a 1-to-1 ratio of CO-to-H₂ is a clean, mediumcalorific value (MCV) syngas.

In an efficient process giving higher heat value syngas, the char shouldbe combusted in an external chamber to heat a thermal carrier such assand, which is then circulated into the gasifier chamber for fastpyrolysis of the biomass. If there is excess heat from such combustion,some of the char can instead be gasified endothermically with steam toproduce additional equimolar CO and H₂ to mix with the volatiles. Excesssteam needed for this process also has the side effect of increasing theH₂ to CO molar ratio in the raw syngas via the water-gas shift reaction.This approach reduces slightly the heat of combustion of the resultingsyngas due to increased CO₂ levels.

To produce a MCV gas at 1.0 bar without active use of oxygen to crackthe tar conventionally requires using a circulating fluidized bed (CFB)(e.g. molten metal bath) with circulating sand and/or catalysts, andsteam injection from the bottom of the gasifier chamber into the biomassfeedstock. These and other fluidized bed concepts require separationdevices for cleaning out the residual tar, soot, and undesirable gasesin the “crude” syngas which has not been able to reach equilibrium ataround 1,000° C. and 1.0 bar pressure. Conventional approaches toachieve fast pyrolysis of biomass and the corresponding MCV syngas atatmospheric pressures cannot contend with the gumming of the processesby the constantly changing tar component. Nor can conventional processesefficiently handle the char component. In these processes, sand as aheat carrier has an advantage in dealing with gumming problems. Thegummed char on the sand particles can be combusted and then the hot,cleaned sand is recycled through the process.

The present invention improves conventional MCV syngas technologies bypyrolyzing a dried biomass reactant into gaseous form more completely.In complete gasification, the chemical makeup of lignin andholocellulose leads to additional methane in the syngas. The overalltheoretical heating value of the resulting syngas (based on theempirical chemical formulae for cellulose, etc., given above) is 20.0MJ/m³. (Pure methane has a corresponding value of 38 MJ/m³.) Under flashpyrolysis conditions, the yield of char using woody biomass (90 wt %birch and 10 wt % aspen; 25.4 wt % lignin and 74.6 wt % holocellulose)reached an averaged value of 10.4 wt % and was independent of: (1) thefluidizing gases, (2) pressures greater than 1.0 bar; and (3)temperatures greater than 650° C. The overall char yield of 10.4 wt %corresponds to 41 wt % char lignin and 0 wt % char holocellulose of theselected wood. This is in agreement with existing data on flashpyrolysis of cellulose and lignin as isolated components. See Fushimi etal. (2003) Ind. Eng. Chem. Res., 42:3929-3936.

The Present Invention:

A major improvement on the current flash pyrolysis technology is toeliminate the need for an external water source and separation devicesby radically altering the gasifier and combustion chambers. Asignificant advantage of the invention is related to its economics: itreduces the expense associated with maintaining separation devices anddoes not require access to water. Thus, the apparatus is far cheaper toassemble, operate, and maintain as compared to conventional gasificationdevices. Increasing the gasifier chamber temperature to about 1,000° C.,and setting the pressure to about 10 bar leads to complete CO₂ and H₂Ogasification from within the biomass within seconds, rather thanminutes. The presence of CO and H₂ in the product gas stream has aninhibition effect on the gasification of wood charcoal. Thus, at about10 bar and less than about 800° C., the chemical equilibrium in theproduct gas stream is shifted in the direction of significant amounts ofCO₂, H₂O, and CH₄, to promote maximal reaction with the carbon in thefeedstock. At temperatures approaching or exceeding about 1,000° C. thechemical equilibrium shifts to significant amounts of H₂ and CO, therebyrequiring an overabundance of H₂O (from process gas) to react withresidual carbon and CH₄ to yield CO and H₂. Alternatively oxygen gas ormetal oxides may be utilized to reform the residual CH₄ and carbon intoCO and H₂.

These factors support the approach utilized in the present invention,specifically: (1) flash pyrolyzing dried and compressed feedstock wafersby direct contact with a molten metal bath thermostatically maintained atemperature of between about 800° C. and about 1,000° C.; (2) gasifyingthe char and tar within the growing bubbles rising through the moltenmetal; the bubbles provide sufficient pressures (up to about 10 bars)and reaction times (about 10 sec) to consume the char and tar completelyby residual gases present in the bubbles. and (3) a shifting of thechemical balance in the product stream to CO and H₂ due to the slowlydecreasing pressure and increasing temperature in the rising bubble,which also allows reducing the active pressurization of the gasifierchamber.

Optionally, steam may be added to the forming product gas bubbles toenhance the gasification rate of the char. However, injecting steamdecreases the heating value of the resulting product gas by increasingthe CO₂ concentration.

Another fast pyrolysis version of the present invention is to pyrolyzethe reactant dry biomass in a molten metal bath at a relatively lowtemperature, about 350° C. The relatively stable tar and gas are thenconveyed away from the metal screens at temperatures above at leastabout 200° C. The gases are then mixed with process gas for pumping athigh pressures through a pipe in the high-temperature liquid metal. Thisheats the process gas. The char produced is crushed and conveyed througha lock valve for where it is picked up by the hot, high-pressure processgas. The char and process gas is then converted to syngas in agasification tube imbedded in the molten metal bath.

In this version of the invention, the molten metal is stationary andisolated in each chamber. All of the carbon in the feedstock isconverted into gaseous form. The process is superior to conventionalpressurized processes that generate MCV syngas because of its moreeffective use of the carbon in the feedstock and the smaller facilityfootprint that is achieved by using a molten metal bath.

Although other liquid-metal-based organic gasification processes hasbeen proposed, none has deliberately achieved flash pyrolysis ofthermally thin solids, and then used the rapidly emerging gas bubble tocreate an initial compression wave whose expansion causes completegasification of the char and tar components by residual gases. Thus, thepresent invention provides an efficient, clean and high heating valuesyngas. The product syngas can be used for any number of purposes,including: (1) firing the external burner for the reaction chamber, (2)creating synfuel with specialized Fischer-Tropsch reactions; (3)generating electricity in a compact Solid Oxide Fuel Cell; and the like.

Because the apparatus required to execute the process has a very smallfootprint (relatively speaking), the inventive method can be implementedin a self-powered mobile unit. Cellulosic feedstock is introduced to theunit, and is converted to synfuel, electricity, cooled N₂/CO₂ exhaust,and excess water for irrigation. A portion of the synfuel is backwardintegrated to power and transport the mobile unit.

Continuous Gasifier—First Embodiment:

A first version of the invention is a continuous gasifier comprisingfour main chambers, each chamber having a distinct function. Thefollowing discussion is made in reference to FIG. 1, which is aschematic rendering of this first embodiment of the invention. A stirredmixing and drying chamber 10 mixes the biomass with a molten metal at atemperature range that causes rapid water evaporation from the biomass,yet is below the degradation temperature of the biomass. Thistemperature range is from 100° C. (i.e., the boiling point of water) toabout 300° C., with a temperature of about 200° C. or less beinggenerally preferred. Preferably, the biomass is inserted into mixing anddrying chamber 10 at atmospheric pressure, near the bottom center of thechamber. The chamber's mixing blades ensure that the floating biomass isadequately mixed with the molten metal-biomass slurry exiting thechamber.

The molten metal-biomass slurry is then transferred under high pressureto the bottom center of a high-temperature pyrolyzing chamber 14. Thechamber 14 contains molten metal and is maintained at a temperature ofat least about 800° C. The transfer can be accomplished using anytransfer mechanism and/or conduit now known or developed in the futurefor moving molten metal slurries, such as slurry pump 12 and conduit 13.For purposes of brevity, several pumps, conduits, and transfermechanisms are mentioned throughout the description of FIG. 1. All ofthese pumps, conduits, and transfer mechanisms are conventional indesign. Thus, moving the molten metal, gases, ash, slag, and the likefrom chamber to chamber can be accomplished using any mechanism nowknown or developed in the future for moving liquids, gases, and solidsfrom place to place. Additionally, the system can be engineered to takeadvantage of gravity, thus eliminating the need for one or more of pumps12, 16, and/or 28. The pumps are depicted in FIG. 1, however, to clearlydelineate the direction of travel of the various materials.

The resulting bubbling producer gas reacts with (and partially gasifies)char and residue at the bottom surface of each bubble. Transfermechanism (slurry pump) 16 and conduit 17 are provided for insertingpressurized hot process gas (comprising heated steam, recycled gas,stranded methane, or a combination thereof). The process gas is providedto augment char gasification and hydrocarbon reforming in the bubbles.The moving pyrolysis products and hot molten metal are then inserted viahigh pressure conduit 18 into an even hotter gasification chamber 20that accommodates the generally longer gasification reaction times.Syngas is formed in gasification chamber 20 and migrates to the top ofthe chamber, where it is removed via conduit 22 and inserted into aseparator 24, such as cyclone. A combustor 94 is provided to heat themolten metal within the gasification chamber 20. A heat exchanger, 15,is provided to backward integrate excess heat from the gasifier 20 tothe pyrolyzing chamber 14.

After removal of syngas from the top of the gasification chamber 20 intothe separator 24 (via conduit 22), the syngas can be used for anydesired end purpose. Two exemplary uses are depicted in the upperright-hand corner of FIG. 1. The separator 24 functions to remove anyremaining particulates from the product gas. The separator 24 is cooledsufficiently to condense any metal vapor, which then re-circulated tothe pressurized pyrolyzing chamber 14 via conduit 26 and valve 27. Theremoved particulates are collected in ash box 80. The syngas at thispoint is quite clean due to the cleansing action of the liquid metal andhigh temperatures in the gasification chamber 20. The syngas can be used“as is” at this point, or passed through a carbon/ceramic filter ifhigh-purity syngas is required. All or a portion of the syngas exitingthe separator 24 can, for example, be used to power a generator 100, inwhich case the entire apparatus comprises an integrated gasificationcombined cycle (IGCC) generator. Alternatively all or a portion of thesyngas exiting the separator 24 can be fed to a reactor 40 forFischer-Tropsch synthesis (or any other suitable reaction).Fischer-Tropsch is presented in the figure as an exemplary reaction. Theproducts of Fischer-Tropsch synthesis, some of which are shown in box110, can then be used in any desired fashion (e.g., as liquid fuels,fuel additives, lubricants, etc.)

Molten metal from the gasifier 26 may also be recirculated back into thepyrolyzing chamber 14 by means of conduit 26 and valve 27. Some ash andcarbon residues are drawn into the circulating molten metal. To removethis ash and residue, valve 27 also enables the circulating metal to bedirected to a separator, such as the skimming tank 30. The molten metalcan be transferred by transfer mechanism (slurry pump) 28. The skimmer30 is provided to remove unreactive ash from the circulating moltenmetal. Clean metal is then recycled back into the mixing and dryingchamber 10 via conduit 32.

A reservoir 70 and valve block 90 are provided to contain and directprocess gas, excess steam and water, and/or air to various parts of theapparatus. These gases are directed to their desired location by conduit91, 92, and 93. For example, air, water, or process gas can be directedinto the gasification chamber 20. Similarly, if desired, natural gasfrom an external source 60 can be introduced into the process gasreservoir. Adding natural gas may be desired to increase the content ofhydrogen within the gasification chamber 20.

Choices of Molten Metal:

The heat transfer carrier (molten metal) must remain a heavy liquid overa very wide temperature range. It also must be relatively non-reactiveand non-evaporative under the operating conditions. The preferred metalis preferably a low-melting point metal, such as gallium (m.p. 29.8°C.), indium (m.p. 156.6° C.), lead (327.5° C.), bismuth (271.5° C.), oran alloy comprising one or more of these metals. The preferred alloyscomprise binary mixtures of Ga and In or Pb and Bi. Ga 75.5/In 24.5metal alloy is most preferred because it offers superb physicalcharacteristics: a melting point (m.p.) of 16° C. and boiling point(b.p.) greater than 2006° C. Pure Ga is equally preferred toGa-containing alloys, but is more costly than most Ga-containing alloys.The Ga/In alloy is also preferred because it is a liquid at roomtemperature. Thus a steam jacket is unnecessary to preheat and melt themetal alloy to start-up the biomass conversion process.

This self-starting feature reduces the overall size of the gasifier.Also, because the apparatus does not require a steam jacket,interruptions in gasifier operations have minimal impact onefficiency-it is not such a daunting task to cool the apparatus formaintenance, and then to bring the apparatus back up to operatingtemperature.

Other suitable metal alloys that can be used in the present inventionhave melting points above room temperature, and thus require using asteam jacket to prime the process. Thus, for example, indium has both alow reactivity and a suitably low melting point to be used in thepresent invention (m.p 156.6° C.; b.p. 2006° C.). Indium performs on anequal footing with both pure Ga and Ga-containing alloys, but iscurrently more expensive the either alternative (and is thus lesspreferred purely on economic grounds).

A non-lead, low-reacting, lower-cost metal alloy that can be used in thepresent invention is Bi 67/In 33 (m.p 109° C.; b.p. 1551° C.).Bismuth-indium alloys offer a wide non-degradation temperature range,with a suitably low melting point. The low melting point is a plusbecause it simplifies preheat process priming.

While lead and lead-containing alloys are less preferred because oftoxicity concerns (and the concomitant regulatory hurdles involving theuse of lead), lead and lead alloys function very well in the presentinvention (and are actually preferred in economic terms). At roughly$24/lb at current prices, lead and lead-containing alloys such as Bi56/Pb 44 (m.p. 124° C.; b.p. 1551° C.) are very low-cost alternatives ascompared to the metals previously described.

Other metal alloys having higher melting temperatures can also be used,provided that the biomass feedstock has a degradation temperature thatis greater than the melting point of the alloy. As a practical matter,the molten metal should be selected from an element or alloy comprisinga metal selected the group consisting of Ga, In, and Pb, as well as BiCd, Sn and Tl and combinations of any of these. If a higher meltingpoint alloy is used, the pump 12 and conduit 13 must be chosen carefullyto accommodate the higher temperature ranges. Thus, the invention willfunction with any metal or metal alloy that melts at a temperature lessthan the degradation temperature of the biomass reactant, which isnon-reactive, and which has a boiling point greater than about 1,200° C.(and preferably greater than about 1,500° C.). Low or no toxicity is aplus, but not required.

Molten salts with a narrow liquid temperature range can be used in placeof molten metals. For example, salts (and other ionic liquids) having amelting temperature below about 250° C. and boiling points above about1,000° C. can be used instead of a molten metal. Many salts, includingchlorides, nitrides, fluoroborates, and the like, fall within thisdescription. For example, the eutectic mixture CuCl (65%)-KCl (35%) is asuitable molten salt that can be used in the present invention. It has amelting point of 150° C. and a boiling point of about 1,300° C. Adistinct advantage of using molten salts or ionic liquids in place ofmolten metals is that it reduces the amount of potentially toxic heavymetals in the ash by-products. Molten ionic liquids for use in theinvention need not be eutectic mixtures. A very large number of suitablesingle salts, binary salt mixtures, and tertiary salt mixtures have beencharacterized that fall within the parameters of having a meltingtemperature below about 250° C. and boiling points above about 1,000° C.Reference libraries containing thermodynamic data and phase diagrams areavailable commercially from many sources, for example, Material ScienceInternational, GmbH, Stuttgart, Germany.

Temperature Ranges:

The preferred temperature ranges for the four chambers are as follows:For the mixing and drying chamber 10 and the skimming chamber 30, thelowest temperature should be about 10° C. over the melting point of thealloy used. The highest temperature should be no greater than about 20°C. below the degradation temperature of the biomass feedstock.

For the pyrolyzing chamber 14 the lowest temperature should be thetar-cracking point (at least about 800° C. for woody feedstocks). Thehighest temperature within the pyrolyzing chamber 14 should be less thanor equal to the temperature within the gasification chamber 20.

For the gasification chamber 20, the low temperature must be equal to orgreater than the high temperature within the pyrolyzing chamber 14. Thehigh temperature within the gasification chamber 20 should not be sohigh as to unduly shorten the lifetime of the equipment. Also thetemperature should not so high as to melt the ash into clinkers (i.e.irregular, vitrified clumps of ash). In practice, the high temperaturein the gasification chamber should not exceed about 1,200° C., andpreferably should not exceed about 1,000° C. It is possible to achievegood gasification results at temperatures of about 800° C. whencatalysts are used in the gasification chamber. Alternatively, oxygenand steam may be added to the raw syngas to reform CH₄ in a secondarygasification sub-chamber within the gasification chamber 20. Thisenables temperatures within the secondary gasification sub-chamber toexceed 1,200° C., while the liquid metal within the primary gasificationchamber remains at a temperature below 1,000° C. Doing so limits theconcentration of vaporized metals and prevents the formation of ashclinkers.

Choices of Pressures:

The pressure ranges for the four chambers are as follows: For the mixingand drying chamber 10, the lowest pressure is atmospheric pressure andthe highest pressure is the upper pressure limit that can be toleratedby the equipment used to feed the chamber 10. The pressure in chambe 10,should be at least about 50% less than the pressure in any of thepyrolyzing chamber 14, gasification chamber 20, and skimming chamber 30.

The pressures within the pyrolyzing chamber 14, the gasification chamber20, and the skimming chamber 30 are dependent, in part, on how thesyngas produced is to be used. For example, if the syngas is to becombusted in an integrated gasification combined cycle generator (IGCC),the pressure in these three chambers should be about 5 to 15 atm. If thesyngas is to be fed directly to an internal combustion engine, thepressure in these three chambers should be from slightly aboveatmospheric to about 3 atm. If the syngas is to be used for downstreamFischer-Tropsch synthesis, the pressure in these three chambers shouldbe from about 15 atm to about 30 atm. Regardless of the ultimate use ofthe syngas, to ensure safe operating conditions, the highest pressurelimit in any chamber must not exceed the safety margin below the burstpressure of the component within the system having the lowest burstpressure rating.

Choices of Gasifying Agents, Augmentation:

The products of pyrolysis formed in the gasification chamber 14 aredeveloping producer gas and floating char. Both components are utilizedas reactants in the gasification chamber for ultimate conversion intosyngas. The primary gasifying agent for use in the present invention issteam because it is most readily available and has the least impact onthe BTU value of the resulting raw syngas. The amount of steam injectedmust be balanced against two competing goals: (1) gasifying as much charas possible, without (2) reforming the methane and hydrocarbons that arealready present in the raw syngas. Balancing these two competing goalsyields the highest BTU producer gas possible, without reforming themethane and hydrocarbons.

The equivalent moisture content required to optimize the yield of syngasis dependent on the feedstock. For wood, sugars, and the like, little orno steam needs to be added. For carbon (i.e. coal), greater than about108% equivalent moisture content should be introduced to thegasification chamber 20. For generic wood charcoal, greater than about81% equivalent moisture content should be introduced to the gasificationchamber 20. For plastics, such as poly(methyl methacrylate) (PMMA),greater than about 6% equivalent moisture content should be introduced,etc. The highest value of steam addition depends on maximizing H₂ and COin the product gas and minimizing C, CH₄ and CO₂. In approximate terms,these equivalent moisture content values correspond to 0% for sugar,greater than about 11% for cellulose, greater than about 25% for wood,greater than about 150% for carbon (coal), greater than about 144% forgeneric charcoal, and greater than about 54% for PMMA, etc.

The gaseous augmentation with H₂ and O₂ to promote exothermic reactionswithin the gasification chamber 20, or metal-based catalystaugmentations are not preferred, and in the preferred versions areabsent entirely. In the preferred process, the process proceeds in theabsence of added H₂ and added O₂. However, when using a feedstock thatis difficult to gasify, H₂ and/or O₂ may be used as follows: (1) H₂ andO₂ may be combusted to generate localized heat and/or to providesuper-heated steam; or (2) H₂ may be inserted into pyrolyzing chamber 14to assist in converting carbon to methane. At the same time, asufficient amount of O₂ is then introduced into the secondarygasification sub-chamber of chamber 20 to convert the methane to syngas.The potential for cold spots in the reactor (which contribute to theformation of creosote from tar or powdery carbon—common problems inother reactor designs) is eliminated due to the high thermalconductivity of the molten metal.

The gasification reactions in chamber 20 may, however, be augmented withstranded methane feedstock, CH₄, from source 60. The added methanebeneficially results in sufficiently high H₂ concentrations in the hotpressurized process gas to consider isolating only the H₂ portion foruse in the combustor 94. In this approach, the flue gases vented to theatmosphere are comprised almost entirely of N₂ and H₂O. All orsubstantially all of the carbon from the biomass reactant, and thecarbon from the introduced methane is converted to syngas. The output ofCO₂ from the Fischer-Tropsch synthesis is completely recycled byinserting it into the process gas. The CO₂ is then reacted with asufficient methane feedstock to form mainly 2 CO+2 H₂. Thus, all of thecarbon in both the biomass reactants and the stranded methane feedstocksare converted to synfuel. In this fashion, the production of methanefrom landfills, livestock activities, vegetation decay, and othersources can be prevented from contributing to atmospheric warming. Ofcourse, subsequent combustion of the synfuel itself will yield CO₂. CO₂,however, but is more easily recycled from the atmosphere (by theactivity of photosynthetic plants) and has a much lower impact on globalwarming as compared to methane.

Choices of the Burner:

The structure and type of combustor 94 for use in the invention is notcritical so long as the combustor can heat and maintain the molten metalin gasification chamber 20 at the required temperatures. It ispreferred, however, that self-sufficiency and high efficiency at lowcost be achieved when the off-gas from a one-pass Fischer-Tropsch

Synthesis (FTS) reaction is used to fire the burner and the process heatfrom the FTS reaction is used for powering the integrated system. InFIG. 1, it can be seen that the off-gas from the FTS reaction iscollected at reservoir 50 and then introduced to the reservoir 70 forinjection into the combustor 94 via conduit 95, valve block 90, andconduit 92.

Choices of the Feedstock:

There are no limitations on the carbon-based, biomass feedstock mixes ormoisture contents, as long as the restrictions on temperature, pressure,gasifying agents, and molten metals noted earlier are observed. At aminimum, however, the feedstocks should be chopped into thermally thinchips. This both improves heat transfer and allows the biomass to beaugered into chamber 10 at an appropriate rate. Care should be taken tomatch the capacity of the skimmer 30 to the chosen feedstock if thefeedstock has a high ash content. Otherwise, the accumulation of ash inthe molten metal will overwhelm the ability of the skimmer to remove theash from the apparatus.

Continuous Gasifier—Second Version

A second version of the present invention also has four main chambersserving different functions (see FIG. 2). However, in the second versionof the invention, the molten metal need not be circulated and is not indirect physical contact with the feedstock. Here, a horizontal augerencased in a porous tube wall 210 is used to move thin layers offeedstock through an evaporation chamber 220 and then through apyrolysis chamber 222, both of which contain static, molten liquidmetal. Air and steam escape from the biomass as bubbles that passthrough the porous tube wall and into the low-temperature molten metalbath. The porous tube wall is of a sufficiently small mesh to preventmolten metal from accessing the auger encased within the porous tube. Alock valve 224 separates the feedstock bin 226 from the inlet into auger210. The gas pressure within chambers 220 and 222 is developed from theevaporated moisture.

After passing through evaporation chamber 220, the horizontal augermoves the now-dried feedstock into a pyrolysis chamber 222 to achievefast pyrolysis at moderate temperatures Like the moisture in chamber220, in chamber 222, combustible volatiles from dried biomass escapethough the porous tube walls and into the hotter molten metal. Catalystsmay be mixed into the stationary molten metal for catalyzing degradationof the volatiles into simpler molecules. This prevents the formation ofcreosote deposits in the “producer gas.” The so-developed producer gasis ideally suited to be condensed as bio-oil 226 for fuel or inserted aspart of process gas 228 for making syngas.

The developing char is moved along and dropped into a verticallydownward auger 230 that crushes the now-fragile remains of the biomassfeedstock. Another lock valve 232 is used to achieve pressures as highas about 20 atm. This pressure is used to move the crushed char into agasification chamber 20. The producer gas may be mixed with the steam(air-removed) from the drying chamber 220, syngas output from separator24, stranded methane introduced from methane source 60, the output fromFischer-Tropsch 40, or steam from a reservoir 50 in such a combinationso as to make an ideal process gas mixture 70 that is pumped to highpressure, about 20 atm.

The process gas is then inserted into a process gas tube 234 immersed inthe high-temperature molten-metal bath within the gasification chamber20, causing further beneficial changes to the process gas. The exit ofthe process gas tube 234 is at high pressure, as well as athigh-temperature. This high-pressure and high-temperature gas exitingtube 234 entrains the crushed char exiting from the second lock valve232 and conveys it into a gasifying horizontal tube 236 immersed withinthe high-temperature molten-metal bath within chamber 20.

The endothermic heat required for reforming the process gas andgasifying the crushed char is provided by tubular combustor 94 disposedwithin gasification chamber 20, or can be provided directly bycombusting H₂ and O₂ (in, for example, a micro-chamber) to makesuper-heated steam. The drying chamber 220 and the pyrolysis chamber 222are situated above the gasification chamber, with appropriate separationwalls interposed to maintain various required temperatures within theseparate chambers. The raw syngas exiting the gasification tube 236 isinserted into a separator 24 as described previously.

Choices of Liquid Metal:

In the second embodiment, the choice of liquid metal is more flexiblebecause the metal itself is not circulated through the device. Indeed,because of the stationary nature of liquid metal, the metal can beselected based on the needs of the specific chamber where it is beingused. For example, there is far less concerns with using lead in thegasification chamber 20 because the chamber can be hermetically sealed.Also a steam jacket is not needed around the various chambers, becausethis second embodiment of the invention is inherently self-starting.Thus, for example, the unit can be shutdown over a weekend (formaintenance) without losing efficiency. The various chambers should,however, be surrounded by highly insulating coverings to promote highthermal efficiency.

Choices of Temperatures:

The temperature ranges for the four chambers are as follows. For thedrying chamber 220, the lowest temperature should be no less than about10° C. over melting point of the metal disposed in chamber 220. Thehighest temperature should be no more than about 20° C. below thefeedstock degradation temperature.

For the pyrolysis chamber 222, the lowest temperature should be thefeedstock degradation temperature (about 200° C. for wood) and thehighest temperature should be consistent with the desired producer gasto be made. For the gasification chamber 20, the high temperature shouldbe below the point at which the ash melts into clinkers. Practicallyspeaking, the high temperature should not exceed about 1,200° C., anmore preferably should not exceed about 1,000° C. As noted for the firstversion, it is possible to lower the operational gasificationtemperatures by using catalysts.

Choices of Pressures:

The pressure ranges for the four chambers of the second embodiment areas follows: For the drying chamber 200 and the pyrolysis chamber 222,the lowest pressure is atmospheric pressure; the highest pressure iswhat can be tolerated by the lock valve 224 and the biomass auger 210.The lowest pressure in the gasification chamber 20 and separator 24 isagain dependent on the use to which the syngas will be put. Thesepressure ranges are the same as those given above for the first versionof the invention.

Choices of Gasifying Agents and Augmentation:

The primary gasifying agent in the second version of the invention issteam, again because it is most readily available and has the leastimpact on the BTU value of the resulting raw syngas. These values arethe same as given above for the first embodiment of the invention.

Likewise, augmentation with added methane is as described in the firstversion of the invention. As in the first version of the invention,augmentation with added H₂ and/or O₂ can be beneficial in certaininstances.

Choices for the Combustor:

The second version of the apparatus can use any combustor that canachieve the required maximum temperature in the gasification chamber 20.However, self-sufficiency and high efficiency at the lowest cost isachieved when the off-gas 50 from a one-pass efficient Fischer-TropschSynthesis (FTS) reaction is used to fire the combustor 94 and theprocess heat from the FTS reaction is used for powering the integratedsystem.

Choices of the Feedstock:

There are no limitations on the carbon-based, biomass feedstock mixes ormoisture contents, as long as restrictions on temperature, pressure,gasifying agents, and liquid metals are observed. The feedstocks shouldbe chopped into thermally thin chips that can be easily augered into thedevice at an appropriate rate.

Tables 1 and 2 present data for the net reaction of woody biomass toethanol and the net reaction of woody biomass to octane, respectively,for various gasification technologies. The present invention improvesupon prior art gasification technologies by obtaining higher efficiencylevels and does not utilize an external water source. The steam forinjection in the present invention is provided by recycling the evolvedsteam captured in the first molten metal bath and from the waterby-product of Fischer-Tropsch synthesis.

TABLE 1 Net reaction for woody biomass, C₆H₉O₄, to ethanol, C₂H₅OH. FuelEffi- Produc- Technology ciency tion Level Per- H₂ C₂H₅OH H₂O CO₂Gallons/ Of Gasifier cent Moles Moles Moles Moles DryTon Current CFBs 500 1.04 −0.88 0.92 100 and Flue Output 2.25 3.0 Self-Sufficient 80 0 1.66−1.4 1.46 161 Heat and 0.9 1.2 Flue Output Use External 100 0 2.08 −1.751.83 202 Heat and External Water Use External 144 −5.5 3 1 0 291 Heatand External H₂

TABLE 2 Net reaction for woody biomass, C₆H₉O₄, to iso-octane, C₈H₁₈.Fuel Produc- Technology Effi- tion Level ciency H₂ C₈H₁₈ H₂O CO₂Gallons/ Of Gasifier Percent Moles Moles Moles Moles DryTon Current CFBs50 0 0.25 0 1.0 68 and Flue Output 2.25 3.0 Self-Sufficient 80 0 0.4 01.6 109 Heat and 0.9 1.2 Flue Output Use External 100 0 0.5 0 2 136 HeatOnly Use External Heat 150 −6.25 0.75 4 0 204 and External H₂

EXAMPLES

The following Examples are included solely to provide a more completedescription of the invention disclosed and claimed herein. The Examplesdo not limit the scope of the invention in any fashion.

Bench-Scale Test Equipment:

To provide a scale-up relationship with a pilot-scale gasifier, abench-scale reactor according to the present invention was fabricatedand used to test flash pyrolysis results using varying sizes offeedstock wafers and varying feedstock moisture levels. The test deviceincluded a primary molten-metal chamber deep enough to test variousreaction pressures and reaction times. The device likewise included ahost of sensors so as to characterize the process with dynamicmeasurements of heating and syngas bubble growth. The test device alsowas able to measure the contents of the developing and bursting syngasbubble to measure the degree of biomass conversion.

Liquid Metal Bath Chamber and Heating:

The main variable affecting the dimensions of the molten metal bathchambers for compatibility to a pilot-scale test is the rise time andsize of the developing bubbles. Because the syngas present in thebubbles should not react with the liquid metal itself, the chosen metalmust be substantially inert with the chosen biomass reactant. As notedearlier, Sn, Ga, Cd, In, Tl, Pb, and Bi are preferred as the mostpractical metal alloying elements (both technically and economically).It must be noted, however, that elemental tin (Sn) reacts with steam andair at higher temperatures Thus Sn is useful primarily for lowertemperature baths and as an alloying metal, rather than a primary metal.From a technical standpoint, Ga, In, and Tl are ideal non-reactingliquid metals that come from the same column of the periodic table. Froman economic standpoint, however, the very high cost of these metals is apractical consideration.

Elemental Ga has the highest temperature range in which it remains aliquid: from 30° C. to 2,237° C., thus it is ideal for use in thepresent invention. Indium is also ideal; the temperature range in whichit remains a liquid extends from 157° C. to 2,006° C. Non-reacting andlow-costing alloy metals with Pb and Bi are also very good for use inthe present invention. The alloy Bi 55.5/Pb 44.5 (melting point 124° C.,density 10,440 kg/m₃) and Pb 54.5/Bi 45.5 (melting point 160° C.;density 10,590 kg/m₃) are particularly preferred alloys of this type.

Using these densities, and with a goal of achieving a pressure of 10bars above atmospheric pressure at the bottom of the bath equates to achamber height of 9.8 m, which is impractical for bench-scale testing.To make the bench-scale device suitably small, pressured N₂ gas waschanneled to the gas chamber above the liquid metal to obtain thedesired pressure at the immersion depth.

Thus, FIG. 3A depicts a schematic of a bench-top test device that wasused to prove the feasibility, functionality, and utility of the presentinvention. The test device depicted in FIG. 3A was used to determine theextent of pyrolysis and to determine optimum wood chip configuration andthe resulting gas combustion energy content, tar and char formation as afunction of heating rate. As shown in FIG. 3A, the comprises abottle-shaped test section 10, disposed within a suitable heater, 20,and containing the molten metal, such as the eutectic PbBi. A pneumaticpiston 30 with a linear displacement transducer 40 injects the samplefrom the low-temperature top portion 52 to the high-temperature regionbottom portion 54. A gas space 56 above the top of the molten metalcolumn provides for liquid metal surface movements and for gas analysis.

The bottle-shaped construction was determined (via a computational fluiddesign calculation) to maintain a 1,000° C. reservoir at the bottom 54of the test section and a 150° C. melt at the top 56 of the neck of thebottle.

To mimic how the process would be implemented at full scale, the woodsamples were presoaked in the low-temperature PbBi alloy. The presoakmirrors the commercial-scale process in which the biomass reactant ispremixed with a low-temperature molten metal (e.g., at temperatures<200° C., temperatures that cause negligible pyrolysis and oxidation) ofthe reactants. Similarly, the test equipment of FIG. 3A, the reactantcan then be plunged into the lower, hotter section of the reactor. Thismimics injecting a slurry mixture from, for example, chamber 10 in FIG.1, into chamber 14 of FIG. 1. The test reactor of FIG. 3A achievescomparable high heat transfer rates and thus efficient and completepyrolysis. The test device shown in FIG. 3A also allows any watercontent and air initially in the biomass reactants to be bubbled out,thus increasing the combustion energy content of the resulting syngas.The design of the test device allows high-speed insertion of the biomassreactants into the high-temperature portion 54 of the test device. (Thefree surface between the N₂ cover gas above the metal and the moltenmetal itself has already been broken by inserting the reactants beneaththe surface of the metal in the top portion 56 of the reactor.)

The test samples (a wood chip) is placed in a holding cage 34 (with apointed base shield to maintain sample integrity while in motion)attached to the end of the rod 32 connected to the pneumatic cylinder30. A thermocouple (not shown in FIG. 3A) is also inserted down thehollow stainless steel rod and placed at the end next to the test sampleto monitor the temperature as a function of time. The cylinder 30 isoperated by a pneumatic valve and the pressure on the cylinder can beadjusted to measure the effects of varying the rate of insertion (i.e.,different temperature gradients). The estimated minimum full extensiontime of 100 ms to cover 0.3 m corresponds to a 3 meters/sec velocity.

A split radiant heater 20 is placed around the test section in the lowerhigh-temperature region 54. The transition region between regions 56 and54 is insulated and the upper portion 56 is convectively cooled tomaintain a temperature gradient such that at the top of the liquid metalin the reactor is held at about 150° C. Initial conduction andconvection analysis using a commercial computational fluid dynamicsprogram indicated that a suitable temperature gradient is obtained inthe test device and that by necking down the throat of the reactorchamber, two convection cells developed: one in the upper cooled portion56 and one in the high-temperature lower region 54.

The test device is equipped with an array of thermocouples evenly spacedalong the height of the molten metal bath to measure the actualtemperature gradient. As noted previously, an additional thermocouple isalso fed through the injection tube and situated just above the testsample.

The gas space above the liquid metal surface is purposefully small sothat the headspace can be evacuated and pressurized quickly. After thesample is inserted into its cage, the piston 30 is activated to immersethe sample into the top portion 56 of the reactor (150° C. PbBi alloy).The water vapor and residual air in the reactant is allowed to evolve.The headspace is then evacuated and purged with N₂ to prepare forrapidly immersing the sample into the high-temperature region 54 of thereactor. The headspace can be pressurized with N₂ to the desiredpressure at any desired time prior to sample injection. Usingthermocouples and pressure sensors in the headspace, the changing volumeof the evolving gases can be deduced through the gas law. Thus thegrowth of bubbles is monitored indirectly through the movement of theliquid metal surface which decreases the volume of the headspace.Bubble-bursting events are detected by the temperature measurementwithin the gas chamber.

Because bubble movement is inconsistent and has a distribution, anindependent means of measuring the liquid metal surface movement isneeded to monitor remaining bubbles within the liquid metal. This isaccomplished using an X-ray system that has been previously shown tocapture two-dimensional liquid lead heights as a function of time. Therise in the liquid metal surface is linked to bubble volume growth andthe lowering of the liquid metal surface is linked with bubble bursting,all of which can be obtained from the X-ray images. See Anderson et al.(2005). “Liquid-Metal/Water Direct Contact Heat Exchange: FlowVisualization, Flow Stability, and Heat Transfer Using Real-Time X-RayImaging,” Nuclear Science and Engineering 150:182-220.

After bubble bursting is completed, the pressurized gas chamber istapped to fill an evacuated sample bottle in a cooled water bath. Thegaseous content of each sample bottle is then measured and analyzed.Typical analyses include mass spectroscopy and gas chromatography. Thecondensed tar/water portion is dissolved in a solvent for chemicalanalysis.

After a test run is completed, the reactor chamber is carefullydepressurized, cooled, and opened. The linings of the gas chamber, thesample cage, and the surface of liquid metal are examined closely andscraped clean of any deposits. The resulting ash, char, and condensedtar (if any) is collected, weighed, and dissolved in a solvent forchemical analysis. To evaluate the gasification performance, the testedsample is weighed and its chemical and structural composition knownprior to testing.

Using the test device depicted in FIG. 3A., wood samples were pyrolyzedand various measurements taken. FIG. 4 depicts the average normalizedpressure trace for the pyrolysis reaction at three differenttemperatures: 600° C., 800° C. and 1,000° C. To generate these data, thesamples were inserted into the top of the device shown in FIG. 3A. Thedevice itself was charged with a lead bismuth alloy. The lower area 54of the reactor was heated to the desired temperature (600° C., 800° C.,or 1,000° C.). The upper area of the reactor 56 was temperaturecontrolled to remain at 150° C. Each sample was then immersed underneaththe molten metal in the top portion of the reactor. It was allowed toremain in the top portion of the reactor until the evolution of bubbles(steam) ceased. The reactor was then sealed and the sample plunged tothe bottom of the bath using cylinder 30 and rod 32. The pressure wasthen monitored as a function of time.

As can be seen from FIG. 4, complete pyrolysis occurs very quickly. Atall three temperatures tested, a steady pressure trace was achieved inless than about 10 seconds. For the reactions at 800° C. and 1,000° C.,complete pyrolysis occurred in roughly 5 seconds.

FIG. 5 depicts the typical product gas composition for reactions usingwood as the biomass reactant, and pyrolyzing the sample at 1,000° C.Included among the raw gas products are hydrogen, carbon monoxide, andhydrocarbons, thus demonstrating that the process can be used to producesyngas.

FIG. 3B is schematic diagram of a continuous reactor that incorporatesmany of the features of the test apparatus depicted in FIG. 3A. Thereactor shown in FIG. 3B, however, makes better use of gravity to feedthe reactants into the device (thereby limiting the number of pumpsrequired). The device show in FIG. 3B also includes baffle plates withthe molten liquid main chamber to control the velocity of the biomassand gas bubbles within the molten liquid pool.

The apparatus depicted in FIG. 3B includes a reaction chamber 300containing a molten liquid. The designation “TC” throughout the drawingdenotes a thermocouple to monitor the temperature of the device atvarious points. Baffle plates 320 are included within the chamber 300 tocontrol the biomass and bubble rise velocity. A biomass feed inlet 304is provided to introduce the biomass reactants into the chamber 300.Various ancillary control mechanisms are included to control the rate ofreactant introduction into the chamber 300 and the pressure within thechamber. Thus is provided feed-stock pinch valve 310, steam bleed valve312, feed tube isolation valve 314, pressure equalization valve 322, andsteam relief/recycle valve 324. Containment inert gas pressurizationvalve 308 is provided to pressurize the safety container. Unsaturatedbiomass feedstock travels through tube 316 and gradually becomessaturated with steam at distal end 318. The biomass than passes intochamber 300.

At this point, the biomass is introduced into chamber 300, along withhydrogen, water, oxygen, or carbon dioxide, which are introduced intochamber 300 via injection ports 306. Hydrogen may also be introducedinto chamber 300 via feed 326. Syngas formed in the pyrolysis reactionis removed from chamber 300 via valve 328.

The molten liquid bath is maintained via a recirculation circuitcomprising pump drive shaft 330, which is operationally linked to aclean-up loop impeller 336 disposed near the bottom or reaction chamber300. The recirculation circuit can be closed via valve 332. A removablemesh 334 is inserted into the circuit to trap ash and other impuritiesthat are formed within chamber 300. In this fashion, molten liquid isdrawn from the bottom of chamber 300, passed upward through the mesh 334(via the action of the impeller 336) where it is thereby filtered, andthen deposited back into the top of chamber 300. The device shown inFIG. 3B is designed to be operated continuously.

FIG. 6 depicts the results of an experiment wherein gas samples of Ar(86.52%), CO₂ (0.504%), H₂ (3.960%), CH₄ (0.010%), CO (6.960%), and O₂(0.48%) were used to determine the gas reaction rates and hold up in areaction according to the present invention using a molten metal bathcomprising Bi (55.5) and Pb (44.5). The experiments were conducted todetermine if the gases would undergo any significant reactions with themolten metal bath itself. Thus, before and after values were taken tomeasure the masses of each gaseous entity within the metal bath itselfand in the headspace above the molten metal bath. Experiments found thatthere were significant reactions of oxygen with the metal to yield metaloxides, e.g. lead (II) oxide (PbO), etc. However, there were essentiallyno reactions of H₂ or CO with the eutectic alloy at temperatures up to1,000° C.

Efficiency, Emissions, and Economics:

FIG. 7 is a graph depicting net process emissions for the chemicalreactions required to produce diesel (with the formula C₁₅H₃₂) fromwoody biomass, as the biomass energy percentage varies. As can be seenfrom FIG. 7, it is beneficial, from the ecology standpoint, to nudgegasifier productivity to higher values. For example, at 100% biomassenergy conversion to FTS products, the need for oxygen (filled trianglepoints) to oxidize with biomass is, by definition, zero; the productionof water (filled diamond points) decreases to a small 2% emission, theproduction of CO₂ (filled square points) is reduced to 58% emission, andthe diesel output (filled circle points) increases gradually to 40% ofthe biomass (by weight).

At the theoretical limit of the gasifier/synthesis conversion ofbiomass, which for diesel is 147%, all of the carbon in the biomass isconverted to diesel and there is no process CO₂ emission. A net input of24% moisture content of biomass is sufficient to provide water forsplitting into H₂ and O₂ via energy from external sources (not biomass).Because the H₂ is incorporated into the diesel fuel (58% net emission),there will be a net emission of O₂ at 65% (by weight). All of theemission quantities obviously have a linear relationship, from 50% to147% of the biomass energy.

The corresponding idealized fuel production (as gallons per dry ton ofwoody biomass) versus the percentage of biomass energy are plotted inFIG. 8. From this plot, the shipping and storage costs for diesel andgasoline obviously would be much lower, in comparison to ethanol, forthe same amount of fuel energy value.

When the biomass-based biofuel industry expands in the future and thedemand for biomass increases, the cost of biomass feedstocks willinevitably escalate (as a matter of supply and demand). A realisticlong-run value for delivered biomass feedstock in the inventors' view is$75 per dry ton, 2008 dollars (by extrapolating from the data ofWalsh,¹⁸ for a reasonable crop yield of hybrid poplar for variousregions and adding in costs for transportation and an inflation factor).Lower feedstock values (at approximately $45 per dry ton) may beobtained initially when the biofuel industry is in its infancy; however,when the industry ramps up to larger-scale production, the cost ofbiomass feedstock will inevitably increase. The escalation of biomassfeedstock cost is also implicit in the recently published “Billion TonBiomass” report, which projected that ˜1.36 billion dry tons of biomasscould be available in the long run in the United States for use inbiofuels, but it would require the cultivation and development ofdedicated biomass energy crops, such as short-rotation hybrid poplars,willows, and switchgrass.

See Perlack, Wright, Turhollow, Graham, Stokes, and Erbach, “Biomass asFeedstock for a Bioenergy and Bioproducts Industry: The TechnicalFeasibility of a Billion-Ton Annual Supply,” April, 2005, an officialpublication jointly published by the United States Department of Energyand Department of Agriculture, on-line athttp://feedstockreview.ornl.gov/pdf/billion_ton_vision.pdf (lastaccessed April 2008), and in hard copy from the National TechnicalInformation Service. Thus, it is assumed that a sustainable long-runcost for such feedstock crops will be approximately $75 per dry tondelivered.

Therefore, using data from FIG. 8 and the $75/ton biomass costassumption, the biomass supply cost per gallon of synfuel can becalculated at different levels of biomass energy percentage. The resultsof these calculations are shown in FIG. 9. For diesel, the cost ofbiomass supply ranges from $1.21/gal at the current 50% biomass energylevel to $0.60/gal at the 100% biomass energy level, and to just$0.41/gal at the 147% biomass energy level. Compare this to theanticipated coal-to-liquid fuel cost of $1/gal diesel at the plant gate.Although ethanol has a much lower cost, in regard to cost of biomasssupply per gallon, the lower energy value and higher shipping cost ofethanol cancel that advantage.

For a more complete economic assessment of feedstock (input) costs, FIG.10 shows the combined total cost of H₂ and biomass feedstock involved inproducing diesel at different levels of biomass energy percentage. It iswasteful to isolate H₂ from biomass or synfuel to use as a hydrogenfeedstock because it is more efficient to convert most or all carbon inthe biomass into synfuel using external sources of hydrogen. Ashort-term goal for the hydrogen industry (articulated by the U.S.Department of Energy) is to obtain $2/kg of “green” H₂ at the plantgate, and then add a dollar more per kilogram to ship the H₂. Thisconverts, in terms of equivalent lower heating value (LHV) at the plantgate, to $2/gal of diesel fuel, as shown by the square points in FIG.10. The levels at 50% and 80% of biomass energy do not need H₂ as input,but they will have biomass feedstock costs that are much less than whatthe H₂ near-term technology can provide. The U.S. Department of Energy(DOE) website indicates the possibility of $1/kg of H₂ at the plantusing windmill power for the electrolysis of water when co-producingpower for the electricity grid.

As shown in FIG. 10, the total feedstock cost is $1.21 per gallon,regardless of whether the energy content of the feedstock is at 50%biomass energy or at 150% biomass energy, using the $2/kg H₂. However,the three-fold increase in synfuel productivity reduces capital costsand provides greater potential for profit. This scenario would occurwhile paying biomass providers $75 per dry ton of woody biomassdelivered, which should be enough to encourage producers to practiceresource sustainability and permit government to conserve prime woodybiomass for ecological development of habitat, watershed, andbiodiversity. Because it is expected that the future cost to produce H₂will fall below $1/kg, the combined feedstock costs of biomass andhydrogen, on the basis of the cost-per-gallon of diesel, will leaveplenty of room for capital and operational costs to reach a targeted$1/gal of diesel to compete with coal-to-liquid fuels or petroleumsources of motor transportation fuels.

Therefore, in anticipation of the coming hydrogen economy, a gasifier isneeded that can function at up to a level of 150%, and utilize hydrogengas to aids in the total conversion of biomass carbon to synfuel. Thepresent invention is such a device. This is a tremendous advantage ascompared to some existing gasifiers, which must undergo expensivereplacement or upgrading to remain current with the advances in the H₂production and biomass carbon conversions.

Potential for Replacing Fossil Fuels with Biofuels in U.S.Transportation:

A question of overarching concern is whether the United States hassufficient biomass to replace fossil fuels in transportation. It hasbeen estimated recently that the volume of biomass that we can modestlyobtain without affecting any other crop or forest usage, as described inthe “Billion Ton Report, supra, is 1.36 billion dry tons per year forthe United States. This level of biomass production is likely to beeconomically obtainable only if prevailing biomass prices reach $75 perdry ton of biomass delivered to plant.

At the conventional 50% biomass energy level, as shown in FIG. 11, this1.36 billion tons of biomass is only one-third of that needed todisplace the 5 billion barrels of petroleum consumed per year fortransportation fuels in the United States. U.S. Dept. of Energy AnnualEnergy Review 2006, Report No. DOE/EIA-0384 (2006). However, at the 147%biomass energy level, which relies on the use of “green” H₂ and theconversion of all feedstock carbon to synfuel, all of the current liquidfuel transportation needs of the United States could be met via biofuelsproduced from 1.36 billion tons of biomass. Coupled with a significantimprovement in gas mileage, the U.S. could become an energy-exportingnation.

1. A method to convert a biomass reactant into synthesis gas, the method comprising: (a) heating biomass in a first molten metal or molten ionic liquid bath at a first temperature, wherein the first temperature is at least about 100° C., but less than the decomposition temperature of the biomass, thereby yielding dried biomass and steam, and capturing the steam; (b) incorporating the steam from step (a) into process gas; (c) heating the dried biomass in a second molten metal or molten ionic liquid bath at a second temperature, wherein the second temperature is sufficiently high to cause flash pyrolysis of the dried biomass, thereby yielding product gases, tar, and char; and (d) reacting the product gases, tar, and char of step (c) with the process gas from step (b) within a third molten metal or molten ionic liquid bath at a third temperature which is equal to or greater than the second temperature within the second bath, thereby yielding synthesis gas via gasification and reforming reactions.
 2. The method of claim 1, further comprising: (e) combusting a portion of the synthesis gas from step (d) to heat the first, second, and third molten baths.
 3. The method of claim 1, further comprising: (e) combusting an external source of natural gas or hydrogen gas to heat the first, second, and third molten baths.
 4. The method of claim 1, wherein step (b) further comprises incorporating a gas selected from the group consisting of natural gas, hydrogen gas, recycled synthesis gas, flue-condensed water, and combinations thereof into the process gas.
 5. The method of claim 1, wherein in step (e), the portion of synthesis gas is combusted to heat the third molten bath only, and heat from the third molten bath is integrated to heat the second and first molten baths.
 6. The method of any one of claims 1 through 5, wherein: step (a) comprises directly immersing the biomass into the first molten bath; step (c) comprises directly immersing the dried biomass into the second molten bath; and step (d) comprises reacting the product gases of step (c) with the process gas of step (b) within rising bubbles of product gas formed within the third molten bath.
 7. The method of claim 6, wherein the biomass is moved from the first molten bath of step (a) to the second molten bath of (c) in the form of a slurry of molten metal or molten ionic liquid and dried biomass.
 8. The method of claim 6, wherein in step (a), the first temperature is less than about 200° C.; and in step (c), the second temperature is from about 300° C. to about 800° C.; and in step (d), the third temperature is less than about 1,200° C.
 9. The method of claim 6, wherein the first, second, and third baths comprise molten ionic liquid baths.
 10. The method of claim 1, wherein when the first, second, or third baths comprise molten ionic liquid baths, the molten ionic liquid has a melting temperature less than about 250° C. and a boiling point greater than about 1,000° C.
 11. The method of claim 1, wherein the molten metal or ionic liquid in each of the first, second, and third baths is the same.
 12. The method of claim 11, wherein the molten metal in each of the first second, and third baths comprises a metal selected from the group consisting of Ga, In, Pb, and alloys thereof.
 13. The method of claim 11, wherein the molten metal in each of the first second, and third baths comprises a metal selected from the group consisting of Ga, In, Pb, and combinations thereof, further alloyed with a metal selected from the group consisting of Bi, Cd, Tl, and Sn. 14-21. (canceled)
 22. An apparatus for converting biomass into synthesis gas, the apparatus comprising: a first molten liquid bath dimensioned and configured to maintain a molten liquid at a first temperature suitable for drying a biomass reactant without degrading the biomass reactant, to yield dried biomass and process gas comprising water, wherein the first bath is dimensioned and configured to transfer molten liquid and dried biomass contained therein to a second molten liquid bath dimensioned and configured to maintain a molten liquid at a second temperature suitable for fast pyrolyzing the dried biomass to yield gas, tar, and char, wherein the second bath is dimensioned and configured to transfer molten liquid, and the gas, tar, and char contained therein to a third molten liquid bath dimensioned and configured to maintain a molten liquid at a third temperature suitable for reforming gas, tar, and char into synthesis gas, wherein the third bath is dimensioned and configured to transfer molten liquid, tar, and char contained therein to a separator dimensioned and configured to separate tar and char from the molten liquid to yield clean molten liquid, wherein the separator is also operationally connected to the first molten liquid bath and dimensioned and configured to transfer clean molten liquid from the separator to the first molten liquid bath; a conduit operationally connecting the first molten liquid bath to the second molten liquid bath and a process gas reservoir, wherein the conduit is dimensioned and configured to transfer moisture from the first molten liquid bath to the second molten liquid bath and the process gas reservoir; and a conduit operationally connecting the process gas reservoir to the third molten liquid bath, wherein the conduit is dimensioned and configured to transfer moisture from the process gas reservoir to the third molten liquid bath.
 23. An apparatus for converting biomass into synthesis gas, the apparatus comprising: a first molten liquid bath dimensioned and configured to maintain a molten liquid at a first temperature suitable for drying a biomass reactant without degrading the biomass reactant, to yield process gas and dried biomass; a second molten liquid bath dimensioned and configured to maintain a molten liquid at a second temperature suitable for fast pyrolyzing the dried biomass to yield gas, tar, and char; a third molten liquid bath dimensioned and configured to maintain a molten liquid at a third temperature suitable for reforming gas, tar, and char into synthesis gas; a char crusher interposed between the second molten liquid bath and the third molten liquid bath, the char crusher dimensioned and configured to crush char into powdered char; a conveyer assembly dimensioned and configured to: (a) move the dried biomass from the first molten liquid bath to the second molten liquid bath; (b) to move char from the second molten liquid bath to the char crusher; and (c) to move powdered char from the char crusher to the third molten liquid bath; a conduit operationally connecting the first molten liquid bath to the second molten liquid bath and a process gas reservoir, wherein the conduit is dimensioned and configured to transfer moisture from the first molten liquid bath to the second molten liquid bath and the process gas reservoir; and a conduit operationally connecting the process gas reservoir to the third molten liquid bath, wherein the conduit is dimensioned and configured to transfer moisture from the process gas reservoir to the third molten liquid bath. 